Telephone loading unit and method of balancing same



Sept. 22, 1936. J. A. WORCESTER 2,055,189

TELEPHONE LOADING UNIT AND METHOD OF BALANCING SAME Filed Aug. 25, 1954 Aa .44 a, B2 a f o n l a o a a a fr L f@ "T CORAL I :T: 21T;

c 0 f o o c l a o o c A: A, 64 6,

s/DE c/RcU/Tco/Ls VENTOR J. A. WRCESTER By A TTORNEV comprising both? 'phantom and side circuitV coils,

Patented Sept. 22, 15936' TELEIIJQNE LOADING UNIT J osenliA- Worcester-l Middto Bell Telephone Labo t i NewYork, Ns Y.; a corpgrh Application 25, 1934,

' 1o claims. (orig The present invention relates to the, loadingof s'o-cailedf phantoied systems 'v'vhereinM two separate 'telephone 'or other` lines 'areassociated'to derive "a third or; phantonifcireuit, the two line circuits 'being-calledfside circu'its A I Slight circuit "imbalances ifnsuch systems give rise t'crossltalk between the phantnfand side circuits. These "imbalancesP may appear ind'ctance, resistance, rcaiia'ity-orationductance un'- balances'y between different elerneuteA of the systemi; Theft/etai crossstaiklislthe'summauon of the cross-tall;v from thefsesepaiate unbalances and; depending oni the relativemagnitudes may Varyi widelyirbznffiieai'end to"`far end and will vary with frequency;"'Considering a loading u nit the inductancefaiid resistance unbalance's may beneutrauzee 'by'i the. addition@ suitab1epoints of'inductanc 'and resi-stance; respectively, in se-` riesfwiththe. wiridirigsi'larid theselunbalances are A often referred'toas'series'unbalances. 'The mai jor capacity unbalances are shunt unbalances occuringbetween oil windings and either the coreo'r thecasirfig,` theiatterof which' isA generally at ground potentialJf-W """f" f" Methods-heretofore proposed of compensating fpr the vshunt and sriesn unbalnes' individually elaborate testing procedurest Y,

`Itis an object ofthepresent invention to reduce thefcrossftalk' unbalances uinci-iilidually "(an'd the total 'cross-talk)A to',` negligh'lylr 155W' Val-ues" ir'i a' simple` and 'economical n'ialnnerA not requi' theusei of particular winding arrangements; A relatedi objectfis tfreduceto negligibly-low value: both near end'andarend coss-talkiover a wider frequencyf'range thanlheifetoiorei t A' further object "is to f securea "more perfect compensation of unbalances givingrise'to cross:

""Othenobjects andtheiifarious"features and aspects. off 'the inventionwill berrnadeL-'ciear from the following detailed description'withthefadfof the'accompanying drawing,"in whiclm j Fig: `1' isa schematic diagramorfthe windings and: "circuit connections of a`= 'phantm'f'loading Y." .i ,Y m.. .i magma.. Wl" s. gv-

Zris a schematicdiagram'oa cross-.talk measuring bridge forcarry-i'ng outan adjusting methodfaccording totheinverition: 2

Fig. 1 shows the various windings employedfor a complete .phantom loadingfufiit consisting. of twc sidev circuit loading-'coils IZf andsIh for the side `circuits or lines: I Ik' and I t,"- anct ia phantom man@ ` assigner his iiolietiede` Y rik lfaadingv coil I5. The latter coil may comprise ari annular core divided z ijrourid` its peripheryfinto eur'equal winding sections rfquadrants'. lIii `each quadrant tiiei'e is *an 'i-'i'niei'fwindingY next the' core (designatedv by` subscript 'numerals' I *and 2-, for eXampIeQiAi; A'2)`l"an`d'an outer `wifndinggA wound over the inner'wincliig l(designated` by subscripts 3 an'df, a'SVA,A A4) I Thief windings "occupy q,d rats succession aro'llncl1 thehoreV inalphabeti-` quadrant;- B11,1B2 and B3; Bwi'ndingsiirithe next quadrant," etc. "Subscript I (e. "g." Ai)` designates the inner end of an inner winding;A 1 subscript 3 (eFg?;"3.) `designates the inner-fend of an outer windingl` subscripts 2i'and`4 referifto outer ends off'inne'rrand outer windings,` respectively. rfIriJt-hephantoin'fcoiif Eig-J1, all.` windings are appliedtothe` core in-the same winding direction whichcris .'an adyantage"'frm a manufacturing standpoint since: theceils cani be wound by ma#A chine withoutinverting inthe machine."

` if The "principali l'shunt 4capacities between the various. windings, inthe case of"both thesidee circuit 'coils and the phantom coil g are indicatedin thegure by' small dotted 'condensersdr'awnin between the various windings or between a wind` ,w

ing and'the core or? the case, which is groundi-di` Thecapacity betweenswindings appears principal- 1y between the outer layer of an inner winding andi` the* inner 'layeri of the: outer winding that 'is' wound over it, for example,A between turns near the termin'aiv 'A2 andturns near the terminal .A; asshowm.'` A AiIt-,is'desirable that a loading unit be balanced for both"` near end and far'end cross-talkin order thatthe saine unitxniay be used indiscriminately infcircuitswhere either type-fzcross-talkis 'of impltance. Examination' of` formulas `for near ehdiiand-far en'd cross-talkeshows .that` if the admittance unbalancef'is reduced` to zero, the exe pressions'for-botlr'types of crossetalkabecome l identical; A Thezadmittance imbalance is made up of capacitative and conductance unbalances, of whichther'former greatlyl predominates. `It is desirable,-therefore, to reduce? the capacity uni balanceto' Zrof and for avery high degreeof equality of lbalance'for both neagrend and far end clQssftalkto reduce the conductance unbalance tQ-zeroalsol" jf'helinvfltion oiers a methodof reducing both vii 12h65 Capacity-,unbalanceand the "conductance un'i g g phantom and the other side circuit. Using designations, P for phantom, Si for one side circuit and S2 for the other side circuit, the capacity unbalance P to S1= (CAC-f-CDA) (CBc-l-CBD) -I- 1/2 (CAG-CBG) A l P to S2: (CAc-I-CBC) (CBD-i-CDA) -l- 1/2 (CcG-CDG) Where CAC, CDA, Cnc and CBD are respectively the`v` capacity unbalances between the respective junction points A, B, C and D in Fig. 1, and CAcsCBG,V

Coe. and CDG represent the capacityY of the respective line windings to ground. By adjusting these capacities to ground, the last term only of each of the expressions for phantom to side circuit unbalance is changed since: these quantities do not appear in the other terms. Moreover, inv

Y- Yin the expression for P to S1 unbalance, the term Y unbalance capacity effect that may be present between the opposite side of the lineand ground, such as indicated at I6.

Unbalance shunt conductance, indicated at Il',

- is balanced by connectingV a small conductance (high resistance) Il between the opposite line conductor and ground. The capacity I6 and resistance. I1 `Vmay be connected between the side circuit terminals and ground, the phantom coil terminals and ground, or the junction'of the side circuit and phantom coils and ground.

'I'he procedure, for adjusting the circuit to minimize the unbalances will now be described with reference to Fig. 2. By means of the crosstalk bridge illustrated in simplified diagrammatic form, the loading unitis iirst measured and adjusted to reduce the shunt admittance unbalance to zero,that isto compensate for shunt capacity and conductance unbalance. For this purpose key 22 is;closed, shunting out the windings in each of the four sides of the lines. Testing current of suitable frequency from generator I8 is then applied through the resistance arms shown and sincethe series impedance of the various windings is now shunted out, vthe indicating circuits 20 `and 2| show only the eects of shunt unbalances. The circuits 20 and 2| may each be provided with variable capacitiesi for example, a three plate rcondenser with the center plate s -groundedand movable .so that the amount of capacity `unbalance can be determined by adjusting to a minimum indicator reading. The necessary amount of capacity I6 is then connected as in Fig.. 1 to exactly compensateY the capacity unbalance. 'I'he Yminimum indicator current obtainable by this method may be sufficiently small for the intended purposes. If a still lower minimum is desired,v some shunt conductance is connected between the proper side of either or both lines and ground 'as' shown at I1 in Fig. 1, and by this -means the shunt unbalance may be reduced practically to zero.

y :The key 22l is now opened and a test made for theftotal cross-talk unbalance which, after the shunt balance has been made` as described, will consist of series inductance and resistance un-v balance. The amount of series inductance and resistance that must be added to one or the other side of each line to secure a balance can be determined by adjustable inductance and resistance devices in series with the line conductors at some point to the left (in Fig.'2) of the indicating circuits 20 and 2|. The variable inductances used for this purpose may advantageously be of the type disclosed in U. S. Patent to R. M. C. Greenidg'e, No. 1,930,269, October 10, 1933. After the necessary inductance and resistance has been inserted in the appropriate sides of the lines, a substantially Zero indicator reading is obtained Y and the procedure ofl balancing the system has Y been'completed.

As an example' of the results obtained with applicants method, three loading units gave an average phantom to side circuit near end crosstalk of 9.6 cross-talk units before adjustment. Adjustment of the shunt Vcapacity unbalance by the method that has ,been described reduced this gureto 2.7 cross-,talk units. By making suitable seriesrresistance adjustment, the cross-talk was reduced to 0.5 unit.. Use of a conductance to ground as described enabled the cross-talk unbalanceto be brought to 0.3 unit which was the final v alue for both near end and far end crosstalk. In addition it was found ,that with the aid of these adjustments the cross-talk variation with frequency could be virtually eliminated over the voice frequency range.

While the'side-to-side cross-talk is not discussed in the foregoing, this may be kept at suitably low value by, methods known in the art.

The method that has been disclosed of adjust- Ying the shunt unbalances of the phantom coil itself can be used toA advantage for adjusting the assembly of loading units and stub-cable. For

this purpose the connections to the testing circuit of Fig. 2Y are made at Vthe ends of the stub-cable remote from the coils, the stub-cable conductors for one quad being indicated by the dotted line conductors leading from the Yloading unit terminals to the lines I0, II proper.

For example, in a type of loading coil case, such as is disclosed in U. S. Patent to Doering et al. 1,668,710, May 8,1928 in which the coils are suspended from the cover, the entire mounted assembly of coils and ,stub-cable can be balanced up outside the case by measuring up the unbalances of coils and stub-cable in the manner that has been described and connecting the compensating capacities, resistances and inductances as required on the terminal'strips of the individual loading units, after which the coily assembly is lowered into the case. In this manner the capacity unbalances in the stub-cable as well as the unbalancesin the loading unit are compensated for.V

'I'he specic values and details given are not Vto be construed .as 'limiting the invention, the

scope of which is indicated by the claims.

What is claimed is:Y

1. The method of compensating the shunt Y capacity unbalance of a phantom loading unit whose windings are all applied inthe same direction, comprising temporarily effectively removing the. series impedances and'connecting impedance of' suitable magnitude lbetween-one conductor of the line pair and Vground to produce a balanced condition. 2. VThe method of compensating the phantomto-side circuitcross-'talk in a phantom loading coil for oneside Acircuit independently of the phantom-to-side circuit cross-talk for the other side circuit comprising increasing the admittance to ground of one conductor of said rst side circuit.

3. In a phantom loading coil system, a closed core having four winding sections all Wound in the same winding direction to provide loading for a phantom circuit, and means compensating shunt capacity unbalance independent of series impedance unbalance comprising a condenser connected from one conductor of a line pair to ground.

4. A combination, according to claim 3, including also a resistance connected between one line conductor and ground.

5. The method of compensating unbalances in a phantom loading unit comprising first testing for shunt unbalances only in a suitable measuring bridge and neutralizing the shunt unbalances by connecting shunt impedance to ground from one side of either or both side circuits as required and then testing for total unbalance in a suitable measuring bridge and adding series impedance in the necessary lines to compensate the series unbalance.

6. As steps in the manufacture of loading coil systems, the method comprising testing the assembly of loading units and stub-cable for crosstalk unbalances, and compensating such unbalances by connecting to appropriate points in the loading coil assembly the required capacities and/or resistances to balance both the loading units and the stub-cable quads.

'7. The method of compensating the unbalances in a phantom loading unit comprising rst shunting out the series impedances and adding suitable shunt impedance at the proper point or points to compensate the shunt unbalance, then unshunting the series impedances and adjusting impedance in series with the unit to compensate the series unbalance.

8. The method of compensating cross-talk unbalance in a phantom loading unit throughout a wide frequency range comprising supplying testing current in simplex through arms of impedance bridged across the terminals of each side circuit coil, short-circuiting the series impedances ofsaid unit and adjusting the impedance to ground of one side of the appropriate side circuit to secure a balance of the shunt admittances, then removing the short circuit connections and adjusting impedance in series in the appropriate side to compensate the series unbalance.

9. The method of compensating the shunt unbalance of a phantom loading unit comprising shunting out the series impedances of the unit and adjusting the admittance to ground of one side of a side circuit to an appropriate value to produce a balanced condition.

10. A phantom loading coil system according to claim 3 comprising also series impedance of a value to compensate series unbalance.

JOSEPH A. WORCESTER. 

